Aqueous cleaning compositions containing alkaline salts, surfactants and other adjuvants have been recently developed to clean a wide variety of surfaces. These aqueous salt cleaners are particularly advantageous since the cleaners are effective and safe to use, handle and dispose of and, accordingly, can replace the more harmful, environmentally unsafe highly basic or organic-based solvents and cleaners previously utilized. Among the particularly useful aqueous cleaners are those which have been developed by the assignee of the present invention, which are based on alkali metal carbonates and/or bicarbonates.
Separate cleaners have been developed for cleaning different surfaces. One such application involves cleaning flux residues from electronic circuit assemblies. Compositions designed for this purpose are disclosed, for example, in U.S. Pat. Nos. 5,234,505; 5,234,506; 5,549,761; 5,575,857; 5,593,504; 5,688,753; and 5,755,893; all of which are assigned to the assignee of the present invention. The aqueous alkaline salt-based cleaners used for this purpose are marketed under the trademark ARMAKLEEN.RTM.. These cleaners are finding increasing acceptance as replacements for the halogenated hydrocarbon and other volatile organic solvents previously used to remove flux residues, in particular, rosin flux residues.
Other applications for which aqueous alkaline salt-based cleaners find application include the cleaning of glass molds utilized for the preparation of optical lenses, or glass lenses prior to the application of optical coatings thereon. Such glass mold surfaces are subject to the accumulation of residues from the resins used in manufacturing operations and must be cleaned before the formation of lenses.
N-alkyl-2-pyrrolidones have been found to be particularly effective as surfactants in the aqueous alkaline salt-based cleaners utilized for the foregoing and other precision cleaning applications, as well as for heavier industrial cleaning, such as in the automobile parts industry. The N-alkyl-2-pyrrolidones function as solvents and are very surface active. The pyrrolidone ring of the N-alkyl-2-pyrrolidone functions as the hydrophilic head and the alkyl group (R) functions as the hydrophobic tail. One well recognized example of this type of surfactant is N-methyl-2-pyrrolidone.
The N-alkyl-2-pyrrolidones which are particularly attractive for the formulation of water based cleaners are those wherein the attached alkyl group (R) has 7 to 12 carbon atoms. One company which manufactures specialty solvents of this type is International Specialty Products of Wayne, N.J., which offers its Surfadones.RTM., namely Surfadone.RTM. LP 100, in which R=CH.sub.3 (CH.sub.2).sub.7 and Surfadone.RTM. LP 300, in which R=CH.sub.3 (CH.sub.2).sub.11.
Although the N-alkyl-2-pyrrolidones can be effective at relatively low concentrations (e.g. 0.05% in wash waters), both the literature and practical experience show that their solubility is severely limited in aqueous based systems. International Specialty Products, for example, indicates that single phase systems are produced with concentrations of LP 100 up to 0.12% and LP 300 up to 0.002%. Homby, J. C. and Domingo, J., "Surface Active Agents," Soap/Cosmetics/Chemical Specialties, September 1992, incorporated by reference herein. These maximum solubilities are quite low. In addition, practical experience has shown that higher concentrations (e.g., 0.2 to 1.0% on a 100% actives basis) of the N-alkyl-2-pyrrolidones may be required for the removal of tough soils. The difficulty of solubilizing elevated concentrations of these materials is found in both the undiluted, aqueous concentrates as received from the manufacturer (also referred to as the "neat product"), and in the corresponding aqueous, diluted solutions.
It has previously been proposed to add a hydrotrope to alkaline salt-based cleaning compositions to maintain the organic constituents thereof, including the surfactants, readily dispersed in the aqueous cleaning solutions and, in particular, in the aqueous concentrates preferred for marketing the compositions. Addition of a hydrotrope permits a user to accurately provide the desired amount of the cleaning composition in an aqueous wash cleaner solution. U.S. Pat. Nos. 5,688,753 and 5,755,893 discussed above (in which one of the present inventors is a named co-inventor) disclose the use, as hydrotropes for salt-containing concentrates incorporating N-alkyl pyrrolidone surfactants, of alkali metal salts of C.sub.7 -C.sub.13 linear monocarboxylic fatty acids; alkali metal, ammonium and alkanolammonium salts of xylene, toluene, ethylbenzoate, isopropylbenzene, naphthalene, alkyl naphthalene sulfonates, phosphate esters of alkoxylated alkyl phenols, phosphate esters of alkoxylated alcohols and alkali metal and ammonium salts of the alkyl sarcosinates.
It is among the objects of the present invention to provide aqueous cleaning concentrates and the corresponding aqueous cleaning solutions, which contain elevated levels of an N-alkyl-2-pyrrolidone surfactant and a particular type of hydrotrope for the N-alkyl-2-pyrrolidone which facilitates solubilizing substantially increased amounts of such surfactant in stable, homogeneous form in such aqueous concentrates and solutions.
It is another object of the present invention to provide a cleaning solution concentrates and aqueous cleaning solutions as just described, which also include alkaline salt and an antifoaming agent.
These and other objects of the invention will become readily apparent upon consideration of the following detailed description of the invention, taken in connection with the accompanying drawings.